(1) Introduction. RCW 84.33.130 requires that the department of revenue annually adjust and certify forest land values to be used by county assessors in preparing assessment rolls. These values are based upon land grades and operability classes. The assessors use maps that provide the land grades and operability classes for forest land in Washington.

This rule explains how the land grades and operability classes provided in the maps used by the assessors were established. The forest land values are annually updated in WAC 458-40-540. For the purposes of this rule and WAC 458-40-540, the term "forest land" is synonymous with timberland and means all land in any contiguous ownership of twenty or more acres which is primarily devoted to and used for growing and harvesting timber and means land only.

(2) Land grades. The land grades are established based upon timber species and site index. "Site index (plural site indices)" is the productive quality of forest land, determined by the total height reached by the dominant and codominant trees on a particular site at a given age.

*1 These are the site indices for one hundred percent stocked stands. Stands with lower stocking levels would require higher site indices to occur in the same land grade.

*2 Marginal forest productivity is land grade 7 operability class 3, in the following townships. All marginal forest productivity in other townships is land grade 8.

Whatcom County - All townships east of Range 6 East, inclusive.

Skagit County - All townships east of Range 7 East, inclusive.

Snohomish County - All townships east of Range 8 East, inclusive.

King County - All townships east of Range 9 East, inclusive.

Pierce County - T15N, R7E; T16N, R7E; T17N, R7E; T18N, R7E; T19N, R9E; T19N, R10E; T19N, R11E.

Chelan County - All townships west of Range 17 East, inclusive.

Kittitas County - All townships west of Range 15 East, inclusive.

Yakima County - All townships west of Range 14 East, inclusive.

(3) Operability classes. Operability classes are established according to intrinsic characteristics of soils and geomorphic features. The criteria for each class apply statewide.

(a) Class 1-Favorable. Stable soils that slope less than thirty percent. Forest operations do not significantly impact soil productivity and soil erosion. Forest operations, such as roading and logging, are carried out with minimal limitations.

(b) Class 2-Average. Stable soils that slope less than thirty percent, but on which significant soil erosion, compaction, and displacement may occur as a result of forest operations.

(c) Class 3-Difficult. Soils with one or both of the following characteristics:

(i) Stable soils that slope between thirty and sixty-five percent; and

(ii) Soils that slope between zero and sixty-five percent, but display evidence that rapid mass movement may occur as a direct result of forest operations.

(d) Class 4-Extreme. All soils that slope more than sixty-five percent.

(e) Variations. Unique conditions found in any one geographic area may impact forest operations to a greater degree than the above classes permit. With documented evidence, the department of revenue may place the soil in a more severe class.